Although human evoked potentials (EPs) have been recorded for 40 years, and EP recovery cycles for more than 30 years, the proposed research represents virtually a new area in the study of abstinence from cocaine abuse. Very little is known about the basic neurophysiological effects, in humans, of the chronic abuse of cocaine or the effects of abstinence from abuse. This study is designed to add to that knowledge base and is based on several related levels of observation: (1) chronic cocaine exposure and withdrawal appears to mimic clinical features of psychiatric disorders, for example, affective disorder or schizophrenia; (2) Somatosensory evoked potential (SEP) characteristics, including recovery cycles, have been shown to be deviant in many psychiatric disorders; 3) SEP characteristics are deviant in early abstinent substance abusers and SEP recovery cycles are deviant in early abstinent cocaine abusers; 4) SEP characteristics tend to normalize with psychiatric treatments, such as antidepressant medications which influence biogenic amine function; and 5) chronic cocaine exposure is said to alter biogenic amine levels. This proposal plans to study somatosensory evoked potential (SEP) recovery cycles at three time points during early abstinence in chronic cocaine users. The dynamic neurophysiological properties of SEP events arising in known neural generators will be measured and related to duration of abstinence. The aims are (1) to measure recovery functions of 7 early SEP components, up to and including negativity at 60 msec poststimulus (N60), (2) to identify which components deviate from normal at initial testing in early abstinent cocaine users, and (3) to determine the extent to which these deviant components change systematically during the first 4 weeks of cocaine abstinence. Eight interstimulus intervals, from 0 to 90 msec, will be used. This project is relevant to both the clinical neuroscience of drug usage and to drug effects on sensory processes. The objective of this project is to contribute toward definition and understanding of basic human neurophysiological mechanisms associated with abstinence from substance abuse, in particular from cocaine.